Conventionally, there is developed a technique in which an exhaust gas purification device (diesel particulate filter) is provided in an exhaust path of an engine and exhaust gas discharged from a diesel engine is purified by an oxidation catalyst or a soot filter of the exhaust gas purification device (see Patent Document 1, for example).
Conventionally, an exhaust throttle device is provided in an exhaust path of an engine to prevent temperature of exhaust gas discharged into an exhaust gas purification device from being lowered, and purification performance of the exhaust gas purification device is maintained.